1. Field of the Invention
This invention relates to a passenger conveyer apparatus having a plurality of steps connected to each other in an endless loop that conveys passengers, and more particularly to a passenger conveyer apparatus that may shorten the depth measurement of a main frame, which is partly laid under a floor of a building, of the passenger conveyer apparatus. In this specification, the word xe2x80x9cstepxe2x80x9d is used to have the broad meaning that includes so-called pallets.
2. Description of the Background
In recent years, with the advent of aging society, it has been discussed whether escalators and moving walkways should be installed in several kinds of facilities. The escalator is one example of a passenger conveyer apparatus that has a plurality of steps like stairs and is installed between upper and lower floors. The moving walkway is another example of a passenger conveyer apparatus that has a plurality of steps or pallets forming a plane surface which conveys passengers.
Public facilities for transportation, such as a train station particularly, promote the installation of such passenger conveyer apparatuses. Most of the train stations mainly promote the installation of escalators because the building of the train station needs to convey people in a condition that passenger paths cross train paths.
FIG. 1 is a side view of a conventional escalator 51. Escalator 51 has a main frame 52, which includes an upper frame 52a, a lower frame 52b and a middle frame 52c. The escalator 51 is bridged in a building 54 by support frames 53a and 53b that are secured to opposite ends of the main frame 52. In FIG. 1, a symbol xe2x80x9cAxe2x80x9d represents a depth measurement of the upper frame 52a, a symbol xe2x80x9cBxe2x80x9d represents a depth measurement of the lower frame 52b, and a symbol xe2x80x9cCxe2x80x9d represents a depth measurement of the middle frame 52c. 
In general, in the case that the escalator 51 is installed in an existing building for a train station, stairs 55 are already set in the passenger path. In some cases, there is no space to install the escalator 51 in a different place from the stairs 55, or the escalator 51 may not function as the passenger path practically even if there is a space to install the escalator 51 in a different place from the stairs 55. Therefore, the escalator 51 is often installed along the stairs 55 after pulling down and altering a part of the stairs 55, a platform 57, and/or a concourse. Further, a roof 56 is usually set above the stairs 55, In the case that the escalator 51 is installed along the stairs 55, it is required to keep a regulation clearance of xe2x80x9cKxe2x80x9d below the ceiling 56. Therefore, an opening is generally excavated in the stairs 55 and the platform 57 in order to put the main frame 52 therein. Hatching portions xe2x80x9cHxe2x80x9d in FIG. 1 are portions to be excavated for the opening.
The depth measurement A of the upper frame 52a and the depth measurement of B of the lower frame 52b depend mainly on a depth of a space for putting a turning system for the steps of the escalator 51. FIG. 2 is a side view showing the upper frame 52a. As shown in FIG. 2, steps 60 are connected to each other in an endless loop and drawn by step chains 61 (only one is shown). Each of the steps 60 has a pair of first guide rollers 62 and a pair of second guide rollers 63. The first guide rollers 62 and the second guide rollers 63 are guided by a pair of first guide rails 65 and a pair of second guide rails 66 respectively. Since the first guide rollers 62 are disposed at left and right sides of the step 60, only one side of the first guide rollers 62 is shown in FIG. 2. Likewise, since the second guide rollers 63 are disposed at the right and left sides of the step 60, only one side of the second rollers 63 is shown in FIG. 2, Moreover, a portion of the second roller 63, is hidden in FIG. 2, and only one side of the first guide rails 65 and second guide rails 66 is shown.
A pair of step chain sprockets 64 is set in the upper frame 52a and disposed at the right and left sides of the step 60 in order to turn the steps 60 over. The step chains 61 are placed around the step chain sprockets 64 respectively. The step chain sprockets 64 are connected together by a sprocket axle 64a. The adjacent steps 60 come close to each other at the time that the steps 60 are turned over by the step chain sprockets 64. Accordingly, it is required to secure a clearance of xe2x80x9cDxe2x80x9d shown in FIG. 2 in order to avoid interference between the respective adjacent steps 60. Therefore, a radius of the step chain sprocket 64 may not be reduced easily. Consequently, it is difficult to reduce the depth measurement of the upper frame 52a. 
The second guide rollers 63 of the step 60 are disposed below a riser 60b of the step 60. Accordingly, the height of the step 60 is determined by at least the sum of a height of the riser 60b and a height of the second guide rollers 63. Further, since the second guide rollers 63 are guided by the second guide rails 66 and turn around the sprocket axle 64a, it is needed to secure a space more than the sum of a diameter of the sprocket axle 64a and double the thickness of the second guide rails 66 between a forward side (upper side) and a backward side (lower side) of the second guide rails 66.
The lower frame 52b has the substantially same structure as the upper frame 52a. Accordingly, the depth measurement of B of the lower frame 52b is determined in the same way as the depth measurement of A of the upper frame 52a. 
The depth of C of the middle frame 52c, as shown in FIG. 3, relies mainly on a depth of a space for putting a guide system for the steps 60 of the escalator 51. FIG. 3 is a side view of the middle frame 52c. To put it in detail, the depth of C of the middle frame 52c is determined by the height of the riser 60b, a diameter of the second guide rollers 63 and a size of a crossbeam 67 secured to the middle frame 52c in the right and left direction against the moving direction of the steps 60.
As described above, in the case that the escalator 51 is installed in an existing building for a train station that has already been built and operated, a lot of costs and time are required to alter a part of the building and to temporarily take some obstructions apart. That is, in case that the escalator 51 is installed along the existing stairs 55, it is required that large openings for putting the main fame 52 of the escalator 51 be excavated in the stairs 55 and the platform 57, thereby greatly increasing a construction cost. If a strengthening material exists under the stairs 55, it is required that the strengthening material be removed and then another strengthening material be newly added, thereby increasing construction costs in most cases. Further, as the building needs massive alteration, a term of the construction extends over a long period of time. In the in station that remains operated, it is needed to take more precautions by separating the construction area, thereby causing inconvenience to users. As a result, the loss to the train station increases.
Japanese patent publication (Kokai) No. 2-243489 discloses a way to reduce the depth measurement of a main frame as explained by using FIG. 4. As shown in FIG. 4, at the time that the step 60 starts to turn over by the step chain sprockets 64, the rear edge 60p of the step 60 makes a locus 72 that transiently overhangs upward. Accordingly, it is required that the height of a floor 73 be determined so as to secure a space for avoiding interference between the steps 60 and the floor 73. According to the above-mentioned JP ""489, the escalator 51 includes lower rails 70a and 71a at a part of each guide rail 65 and 66 respectively for guiding the first guide rollers 62 and the second guide rollers 63 respectively. The steps 60 move downward along the lower rails 70a and 71a before the steps 60 reach to the step chain sprocket 64. As a result, it is not needed to raise the height of the floor 73 in order to avoid the interference between the rear edge 60P and the floor 73.
It is thought that the depth of the upper frame 52a may be reduced by providing the lower rails 70a and 71a, because lowering the height of the floor 73 lowers the depth of the upper frame 52a. However, the present inventors have attempted to reduce the depth of the upper frame 52a by using lower rails 70a and 71a and simply reducing a radius of gyration of the steps 60. The structure of the inventors"" efforts is shown in FIG. 5. According to the structure shown in FIG. 5, the depth of H2 of the upper frame becomes lower compared to the depth of H1. However, this structure causes problems in the upper frame.
For example, it is assumed that the steps 60 turn over clockwise in FIG. 5. In this case, the first guide roller 62a of the step 60a, which is now turning over as shown in FIG. 5, is driven clockwise by a force of xe2x80x9cFxe2x80x9d produced by the step chain sprockets 64. At this time, the second guide roller 63a of the step 60a needs to move to the right until the turning area. That is, a force of xe2x80x9cfxe2x80x9d is needed to move the second roller 63a to the right. However, the second guide roller 63a is dependent on the first guide roller 62a That is, the second guide roller 63a moves by a moving force, which applies to the first guide roller 62a, given by the step chain sprockets 64. Accordingly, since the force xe2x80x9cFxe2x80x9d does not include a constituent of the moving force xe2x80x9cfxe2x80x9d, the step 60a stops at this position. In the final analysis, the present inventors have discovered that the depth of the upper frame may not lower by simply reducing a radius of gyration of the steps 60 with the use of the lower rails 70a and 71a disclosed in JP ""489.
Accordingly, one object of this invention is to provide a passenger conveyer apparatus that may reduce the depth of the main frame.
Another object of this invention is to provide a passenger conveyer apparatus that may reduce installation costs thereof.
The present invention provides a passenger conveyer apparatus, including a plurality of steps, connected to each other in an endless loop, traveling on a forward path, a backward path and a pair of tuning paths connecting between opposite ends of the forward path and the backward path, each of the steps having a step bead, a first guide roller, and a second guide roller disposed apart from the first guide roller in the moving direction of the steps, a step chain coupled to the first guide roller and placed around a step chain sprocket disposed in one of the turning paths, a drive unit configured to drive the step chain sprocket and to circulate the steps, a forward rail configured to guide the first guide roller and the second guide roller in the forward path, a backward rail configured to guide the first guide roller and the second guide roller in the backward path, and a pair of turning rails, configured to guide the second guide roller in the turning paths and connected between opposite ends of the forward rail and the backward rail, having a curving rail formed in a semicircle, at least one of the turning rails forming in a mower such that a line segment drawn between the orbital center of the curving rail and the first center of the first guide roller makes an acute angle with a line segment drawn between the orbital center and the second center of the second guide roller, and that loci made by respective turning motions of front and rear edges of the step tread cross each other.